It's useful to be able to read eBooks in some open format, so you can keep reference information and entertainment on it.

Similarly you can store some maps, knots, first aid info etc in picture form.

Some phones have an FM radio (which generally needs the ear phone lead as an aerial), which could be invaluable for picking up broadcast information in a crisis. Even weather forecasts. Especially if the internet isn't available.

There are apps which will tell you where the sun and moon are, which can help with basic navigation if you don't have a proper compass or GPS.

A camera can be useful. A photograph of the snake that bit you may help the doctor figure out how long you have to live. You can use it to keep records of landmarks, or for evidence after a car crash.

Some phones are designed for survival. Eg http://www.durrocomm.com/lm801rugged.html features include:
Torch Lighting
Laser Pointer
Built in barometer and altimeter
Built in Compass
Built in Thermometer
FM Radio